Modern high speed, high density circuitry often requires contacts with very close center-to-center spacings of less than 0.050 inch. Such close spacing can be achieved by spring probe compression contacts, wherein each contact has a spring biased probe whose tip can press against a conductive pad on a circuit board. U.S. Pat. No. 4,200,351 shows a compression contact wherein a spring-biased plunger projects from one face of a dielectric support to contact a conductive pad on a circuit board.
While compression contacts allow for high densities of contacts, they can create problems. The close spacing of the contacts can lead to crosstalk. Also, if each contact lies close to a grounded shield, the characteristic impedance of the contact may be too low. It may be noted that coaxial cable configurations generally employ three impedance levels: 50, 70, and 93 ohms. Any metal spring around the contact increases its effective diameter and therefore decreases the characteristic impedance. Furthermore, any metal spring can add appreciable inductance to the contact which is detrimental to the transmission of high speed data signals. Many present applications require a pulse rise time of less than 32 picoseconds, which cannot be achieved if there is appreciable inductance. A contact arrangement which allowed close spacing of contacts, while minimizing crosstalk, minimizing inductance, and allowing control of impedance especially to allow for relatively high impedance, would be of considerable value.